IfStatement: 'if' Condition 'then' Statements 'end'
           | 'if' Condition 'then' Statements 'else' Statements 'end';
Statements: Statements Statement | Statement | EMPTY;
Statement: IfStatement;

terminals
If: 'if';
Then: 'then';
Else: 'else';
End: 'end';
Condition: 'cond';
